In a serial printing apparatus such as, for example, a dot printer, an ink-jet printer or the like, an image is formed on a sheet of printing paper by printing an image having a predetermined width a plurality of times on the paper. Therefore, the feeding of paper at intervals corresponding to the predetermined width should be performed with relative precision.
FIG. 6 is a block diagram showing a paper-feed control unit of a conventional image-forming apparatus. FIGS. 4A through 4D illustrate the operation of a paper-feed control unit of an orthogonal-transfer-type image-forming apparatus disclosed in the Japanese Patent Application Laid Open No. H09-230715, in which a toner image is transferred in an orthogonal direction to the paper feeding direction.
In FIG. 6, a printing controller 2 controls a transfer controller 3 for controlling image transfer, and a paper-feed-motor-drive-controller 4. The paper-feed-motor-drive-controller 4 controls the drive of a paper-feed-motor 5. The paper-feed-motor 5 causes resist roller 6 and paper-ejection-roller 7 to rotate. The components shown in FIG. 6, with the exception of transfer controller 3, comprise the paper-feed control unit.
In FIG. 4A, resist roller 6 is disposed upstream of toner image carrier 100 (the paper feeding direction shown by arrow 20) and paper-ejection-roller 7 is disposed downstream of toner image carrier 100. In toner image carrier 100, a toner image is formed corresponding to inputted image data. Transfer-facing-roller 8 performs printing by transferring a toner image, formed in the toner image carrier 100, to a sheet of printing paper 12 by rotating and moving in a direction orthogonal to paper feeding direction 20. As shown in FIG. 2A, printing area P is an area between right end 100a (end at downstream side of paper feeding direction) and left end 100b (end of upstream side of toner image carrier 100) of toner image carrier 100. A transfer plate 9 is pressed by transfer-facing-roller 8 through toner image carrier 100 and printing paper 12. Resist-pinch-roller 10 faces resist roller 6. An explanation of the structure and operation of a chassis supporting transfer plate 9, etc. is omitted. In FIG. 4D, LP represents the length of printing paper 12 in paper feeding direction 20, 12a represents the front end of printing paper 12 of the downstream side of paper feeding direction 20, 12b represents the back end (final end) of the upstream side of paper feeding direction 20, and "A" represents the dimension from resist roller 6 to left end 100b of toner carrier 100 as shown in FIG. 4A.
FIG. 5 is a flow chart showing an operation of a paper-feed control unit of a conventional image-forming apparatus. The operation is described below referring to FIG. 4A through FIG. 4D, FIG. 5, and FIG. 6.
First, paper-feed-motor-drive-controller 4 rotates paper-feed-motor 5 by an A-step (S21). For paper-feed-motor 5, a stepping motor may be used. Following an A-step rotation of paper-feed-motor 5, front end 12a of the printing paper reaches to substantially the same position as that of right end 100a of printing area P of toner image carrier 100. Then, a first transfer is performed (S22) on first printing area P.
Next, paper-feed-motor 5 rotates by a B-step (S23) feeding printing paper 12 by paper-feed-dimension B1. Dimension B1 is equal to the width of first printing area P as shown in FIG. 4B. FIG. 4B through FIG. 4D show the relative movement from the position in FIG. 4A of printing paper 12. In step S24, a second transfer is performed on second printing area P.
Then, paper-feed-motor 5 rotates again by a B-step (S25) for feeding printing paper 12 by a paper-feed-dimension B1. In step S26, a third transfer is performed on third printing area P.
Further, paper-feed-motor 5 rotates by B-step (S27) for feeding printing paper 12 by a paper-feed-dimension B1, and as shown in FIG. 4D, a fourth transfer is performed (S28) on forth printing area W (final printing area). After final printing, the printing paper is ejected (S29).
As shown in FIG. 4D, in the paper-feed control unit of the above conventional image-forming apparatus, because the paper-feed-dimension after the third printing is B1, back end 12b of printing paper 12 arrives at a position displaced by a dimension LL from resist roller 6. In FIG. 4, LL&gt;A, and a paper-feed of dimension LL is performed by paper-ejection-roller 7. Due to the dispersion of the diameter of the roller of paper-ejection-roller 7, however, the paper-feed-dimension may not be accurately B1, and may differ from the paper-feed dimension traversed by resist roller 6, by which the quality of the transferred image may deteriorate. Therefore, it is desirable to make the dimension of paper-feed traversed by a paper-ejection-roller as short as possible.